Method of briquetting ore



Dec. 27, 1966 E. A. PELCZARSKI METHOD OF BRIQUETTING ORE Filed Oct. 21, 1964 age. 3 ua ok INVENTOR. EUGENE A. PELCZARSK/ M/&%

w IV 7235? Attorney United States Patent 3,294,524 METHOD OF BRIQUETTING ORE Eugene A. Pelczarski, West Deer Township, Allegheny County, Pa., assignor to United States Steel Corporation, a corporation of Delaware Filed Oct. 21, 1964, Ser. No. 405,377 4 Claims. (Cl. 75-3) This invention relates to an improved method of briquetting iron oxide fines with a bituminous coal binder.

Before iron oxide fines can be changed to a blast furnace or similar reducing reactor, they must be formed into agglomerates large enough not to be blown from the furnace. The agglomerates must have sufficient mechanical strength to avoid excessive degradation in handling at ordinary temperatures, and also to withstand temperatures and conditions encountered in blast furnace operation. Optionally limestone or dolomite can be included in the agglomerates in quantities to make them sel-i-fiuxing. Briquetting is one of several processes currently used for agglomerating iron oxide fines. Usually a briquetting process involves pressing the fines into pillow-shaped bodies under high pressures in a roll-type press. The fines can be briquetted at high temperatures without a binder, or at lower temperatures with a binder, such as bituminous coal, pitch, molasses, sulfite liquor and others. A bituminous coal binder serves an additional purpose of ifurnishing carbon which can be used in the reducing reactions in a furnace. However, it is difficult to produce coal-bonded briquettes which have sufficient mechanical strength. Unless coal is heated to a temperature at which it is plastic, it does not provide a good bonding action, but at such temperatures it oxidizes readily and loses its bonding properties.

Previously it has been proposed to overcome this diffic-ulty by separately heating iron oxide and preferably flux fines to a temperature above the optimum briquetting temperature and mixing the heated fines with low-temperature coal fines. The mixture reaches an apparent temperature of about 600 to 800 F., and is compacted into briquettes directly following the mixing step while it remains at this temperature. This briquetting method is described more fully and claimed in another application by Brisse and Rohaus, Serial No. 271,938 filed April '10, 1963, now Patent Number 3,174,846. While the method is successful, heating and mixing the particles in separate steps cause awkward handling problems and necessitate extra equipment.

An object of my invention is to provide an improved method of briquetting iron oxide fines with a bituminous coal binder in which the iron oxide and coal are heated and mixed in a single step without destroying the bonding properties of the coal, thereby avoiding the handling and equipment problems of the other method.

A more specific object is to provide a briquetting method which attains the foregoing advantages by virtue of pelletizing a mixture of iron oxide fines, bituminous coal fines and preferably a flux, heating the pelletized mixture to the briquetting temperature, and compacting the heated mixture.

In the drawing, the single figure is a diagrammatic representation of apparatus suitable for performing my briquetting method.

According to the present invention, I feed iron oxide fines, bituminous coal fines, and preferably a [flux to a conventional pelletizing device .10, which can be either a disk or a drum, as known in the art. The iron oxide and flux particles are of a size suitable for pelletizing, commonly minus inch or finer. The coal particles preferably are minus 8 mesh. The mixture has a coal content of about to 15 percent and preferably sufiicient ice flux to make the product self-fluxing. I introduce sufficient water to the pelletizing device to form the mixture into pellets preferably of a maximum size of about inch. The minus 4 inch starting material contains only a small percentage of particles which are close to A inch in size. Some of these particles may not enter into pellets when 1 limit the pellet size to about A. inch, but the number of such particles is negligible.

A conveyor 12 carries pellets from the pelletizing device to a direct gas-fired kiln 13, where I heat them to an apparent temperature of about 600 to 800 F. The heated pellets discharge from the kiln through an insulated chute 14, which carries them directly to a conventional briquetting press 15, illustrated as of the roll-type. Exhaust gases discharge from the other end of the kiln. I compact the pellets into pillow-shaped briquettes under a load of about 30,000 to 65,000 pounds per linear inc-h of eifective roll width and while their temperature remains in the foregoing range. The pellets of course break on reaching the press, but the pelletized form of the mix protects the coal particles against overheating and oxidizing in the kiln. The briquettes discharge from the press to a conveyor 16, which carries them out of contact with air to a suitable cooler, not shown.

As an example to illustrate my invention, I made up two mixtures consisting of 81 percent minus inch iron ore, 5 percent minus inch limestone, and 14 percent minus 8 mesh coal. I pelletized one of the mixtures but not the other, and heated each mixture to about 600 F. is a direct gasafired rotary kiln. I compacted each of the mixtures to form briquettes in a roll-type press. The nonpelletized mix caused serious dust-loading in the kiln, which the pelletized mix avoided. Microscopic examination of the heated mixes as they came from the kiln showed a wide temperature distribution in the coal particles with the kiln feed that was not pelletized. Some of the coal particles were barely heated, while others were heated beyond the temperature of maximum fluidity and had turned into semi-coke. Briquettes containing semi-coke particles were easy to break. Examination of the heated pelletized mix showed less semi-coke, which indicates a more uniform temperature distribution. I also observed less sensitivity to ignition of the kiln charge with the pelletized feed. Apparently a localized reducing atmosphere forms within the pellets by release of volatile matter which prevents oxidation of the coal,

From the foregoing description it is seen that my invention affords a simple method of forming iron oxide briquettes with a bituminous coal binder. By pelletizing the materials before heating, 1 am able to avoid the handling problems encountered in heating the materials separately, yet produce satisfactory briquettes.

While I have shown and described only a single embodiment of my invention, it is apparent that modifications may arise. Therefore, I do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

I claim:

1. A method of briquetting iron oxide fines with a bituminous coal binder comprising pelletizing a mixture of iron oxide and bituminous coal particles to form pellets having a coal content of 5 to 15 percent, heating the pellets to a temperature in the range of about 600 to 800 F., and compacting the pellets into briquettes directly following the heating step while their temperature remains in said range.

2. A method as defined in claim 1 in which the mixture contains a flux selected from the group consisting of limestone, dolomite and mixtures thereof in proportions to make the briquettes selffiuxing.

3. A method as defined in claim 2 in which the iron oxide and flux particles are minus A1, inch and the coal particles minus 8 mesh, and the maximum pellet size is about A inch.

4. A method of briquetting iron oxide fines with a bituminous coal binder comprising feeding to a pelletizing device minus inch iron oxide fines, minus 4 inch fines of a flux selected from the group consisting of limestone, dolomite and mixtures thereof, minus 8 mesh bituminous coal fines, and water, the coal being in proportions to produce a coal content of about 5 to 15 percent, the flux being in proportions to produce a self-fiuxing product,

forming the mixture into pellets of a maximum size of about inch in said device, feeding the pellets to a di rect gas-fired kiln, heating the pellets in the kiln to a temperature in the range of about 600 to 800 F., transferring the heated pellets from the kiln directly to a rolltype br-iquetting press, and compartin g the pellets into briquettes in said press while their temperature remains in said range under a load of about 30,000' to 65,000 pounds per linear inch of effective roll width.

No references cited.

BENJAMIN HENKIN, Primary Examiner. 

1. AMETHOD OF BRIQUETTING IRON OXIDE FINES WITH A BITUMINOUS COAL BINDER COMPRISING PLLETIZING A MIXTURE OF IRON OXIDE AND BITUMIOUS COAL PARTICLES TO FORM PELLETE HAVING A COAL CONTENT OF 5 TO 15 PERCENT, HEATING THE PELLETS TO TEMPERATURE IN THE RANGE OF ABOUT 600 TO 800* F., AND COMPACTING THE PELLETS INTO BRIQUETTS DIRECTLY FOLLOWING THE HEATING STEP WHILE THEIR TEMPERTURE REMAINS IN SAID RANGE. 